The present invention relates to a horizontal-jointed, continuous nozzle ring for a steam turbine nozzle box.
Nozzle Boxes generally accept steam at four distinct inlet ports. Typically, nozzle boxes are formed from two or more parts which are bolted together to form a complete nozzle box. Within each nozzle box part, steam is first redirected to flow in the axial direction and then accelerated about the axis of rotor rotation via nozzles located in the nozzle box exit plane. The nozzles are carried by a arcuate-shaped nozzle ring segment associated with each nozzle box part. The two nozzle box parts are bolted along their common horizontal joints so as to provide a rigid, stable structure during operation.
In prior art nozzle boxes, the structural thickness of the nozzle box horizontal joint was extended axially along the box and into each nozzle ring segment. This resulting discontinuity in the nozzle ring in the vicinity of the horizontal joint is illustrated at xe2x80x9cAxe2x80x9d in FIG. 4 which shows the toroidal portion of a nozzle ring in the vicinity of a horizontal joint (the toroidal portion of the nozzle ring as shown in FIG. 4 has been stretched out and depicted linearly to clearly illustrate this feature of the prior art). The associated disruption in nozzle air flow in the vicinity of the horizontal joint has proven to be detrimental to overall machine efficiency.
It is an object of the present invention to eliminate the nozzle ring horizontal joint interruption (flow blockage) typical of prior art-nozzle boxes. The present invention provides a nozzle box which increases full-load efficiency in steam turbines by employing nozzle ring segments continuously carrying nozzles, even at their respective horizontal joints, to thereby form a continuous 360xc2x0 ring of nozzles.
Each nozzle box half is comprised of inlet nozzles and a toroidal portion. The toroidal portion comprises three segments, an inlet nozzle box segment, a transition bridge segment, and a nozzle ring segment. Each nozzle box half, is compatible with another nozzle box half so when assembled together a 360xc2x0 ring of nozzles, without interruption at the horizontal joints, results. For each nozzle box half the nozzle ring segment is welded to the transition bridge segment, which is in turn welded to the inlet nozzle box segment.
Two nozzle box halves are then bolted together to form a complete nozzle box having a complete 360xc2x0 ring of nozzles.